The present invention relates to a recording material and in particular to a recording material superior in stability of color imaged portion and unimaged portion.
Recording materials which use a developer which contacts with a normally colorless or palely colored dye precursor to cause the dye precursor to form color are known and widely used as pressure-sensitive recording sheets, photosensitive pressure-sensitive recording sheets, heat-sensitive recording sheets, electro heat-sensitive recording sheets, heat-sensitive transfer sheets, and the like. For example, pressure-sensitive recording sheets are disclosed in Japanese Patent Kokai (Laid-Open) No. 58-217389 and Japanese Patent Kokoku (Post Exam. Publication) Nos. 40-9309, 49-10856 and 52-1327, photosensitive pressure sensitive recording sheets are disclosed in Japanese Patent Kokai (Laid-Open) Nos. 58-16886 and 58-17432, heat-sensitive recording sheets are disclosed in Japanese Patent Kokai (Laid-Open) No. 48-30944 and Japanese Patent Kokoku (Post Exam. Publication) No. 45-14039, electro heat-sensitive recording sheets are disclosed in Japanese Patent Kokoku (Post Exam. Publication) No. 52-44206 and heat-sensitive transfer sheets are disclosed in Japanese Patent Kokai (Laid-Open) No. 60-168690.
In these recording materials, inorganic solid acids, semi-synthetic solid acids, substituted phenols, p-substituted phenol-formaldehyde polymers, metal salts of aromatic carboxylic acids and the like are used as developers which contact with normally colorless or palely colored dye precursor to cause the dye precursor to form color.
Requirements which recording materials should satisfy are sufficient color density and color sensitivity and besides, excellent stability of imaged portion and unimaged portion, especially high light resistance, water resistance and chemical resistance are also essential requirements to be satisfied. The above-exemplified developers have both merits and demerits in their properties.
For example, inorganic solid acids and semi-synthetic solid acids are inexpensive, but adsorb gas or water in the air in storage to bring about yellowing of coated surface or deterioration in color formation properties. Furthermore, exposure to light such as sun light causes deterioration of color image. Substituted phenols is inferior in color forming properties and result in low density of image. p-Substituted phenol-formaldehyde polymers are excellent in color formation properties, but upon exposure to light such as sun light or adsorption of NOx in the air, coated surface is yellowed and color image is also deteriorated. Metal salts of aromatic carboxylic acids are superior in color formation and light resistance and cause less yellowing, but still suffer from the problems in water resistance and chemical resistance.
Especially, chemical resistance is an important requirement for recording materials. When a sheet on which colored record image is formed is stored in a file made of polyvinyl chloride film or the like, plasticizers in the polyvinyl chloride film cause deterioration (discoloration) of image. Further, when the sheet contacts with office supplies such as writing utensils of water or oil ink, vermilion ink pad, adhesives, and diazo developers, and cosmetics such as hand cream and milky lotion, the coated surface (white portion) forms color (so-called fogging phenomenon) and the image area fades in color.
Thus, conventional developers still have problems to be improved and novel developers free from these problems have been demanded.